Prototype 250 GHz Bandwidth Chip to Chip Electrical Interconnect, Characterized With Ultrafast Optoelectronics

We have connected two optoelectronic chips with air-spaced two-wire transmission lines and have observed essentially undistorted transmission of 1.8 ps (FWHM) electrical pulses over propagation distances up to 200 cm. The lines consist of two 0.4 mm (or 0.5 mm) diameter copper wires with centers separated by 1.0 mm. The air spaced two-wire lines show transform-limited TEM mode pulse propagation with very small group velocity dispersion (GVD), and relatively low attenuation. Our achieved performance with a power loss of 5.8 dB/m approaches that needed for mm-wave and THz interconnects. The coupling was enabled by two tungsten probes with 1 μm diameter tips in near-contact (5 μm gap) with the coplanar transmission lines on the transmitting and receiving optoelectronic chips. The air spaced two-wire line's relatively small, measured pulse amplitude attenuation coefficient was 1.31 times larger than the theoretical prediction for the TEM mode. This discrepancy is considered to be primarily due to reduction of the Cu conductivity in the THz skin-depth layer.